Radio frequency multipactor amplifier



Sept. 5, 1939. P. T. FARNSWORTH 2,172,152

RADIO FREQUENCY MULTIPACTOR AMPLIFIER Filed Feb. 21, 1958 1N VHVTOR Bar/4 0 Z Zak/vs WOR TH.

20 fields is not necessary;

EPatented Sept. 5, 1939 warren STATES PATENT OFFICE 2,112,152 mm FREQUENCY mmao'ron AMPLIFIER Application February 21. 1938, Serial No. 191,707

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This invention relates to electron multiplying devices, and particularly to a radio-frequency multipactor amplifier.

The objects of this invention are:

5 To produce an electron multiplier particularly adapted to act as a radio-frequency amplifier; to produce a radio-frequency muitipactor amplifier having a photosensitive cathode; to produce a radio-frequency amplifier using repeated 1 impacts on secondarily emissive surfaces to increase the output current; to provide means for utilizing photo-emission and secondary emission together in a multipactor amplifier; to provide a multipactor amplifier in which the output current is linearly responsive to light directed upon a photosensitive element therein; to provide such an amplifier in a form wherein a signal may be modulated upon the output; to provide a multipactor amplifier wherein the use of focusing to provide. a multiplier amplifier in which multiplication may be started by ionized particles existing therein, by photoemission, or by an electron gun.

Other objects of my invention will be apparent or willbe specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

Various types of electron multipliers. both e..-c. and d.-c., have been developed by me, and those associated with me, forming the subject matter of anumber of United States patents, of which the following are illustrative: Electron 36 multiplying device No. 2,071,515, Oscillation generator No. 2,071,516, and other applications now in prosecution.

The present application is concerned only with a.-c. multipliers, and in the form presented is 40 particularly suited to amplify a radio-frequency carrier and permit modulation of a signal current thereon in a single tube.

In the drawing:

Fig. l is a schematic sectional view of a tube 45 embodying my invention, together with a circuit diagram indicating a preferred mode of operation.

Fig. 2 is a sectional view of my device taken along line 2-2 of Fig. l.

In the arrangement shown in Fig. 1, an evacuated envelope I of glass or similar material has formed at one end thereof a re-entrant stem! terminated by a conventional press 4. An electron gun of conventional type is supported on 55 said stem, having a heater cathode 5 having a resistance coil 6 therewithin and a concave emittingface l. The coil 6 may be energized by a d.-o. current source 9, such as a storage battery,

through leads I 0 and II sealed through press 4, lead III acting also as a support'for the cathode 5. 6 The emitting face I is preferably coated with thermionically active material to increase the strength of current given oif, using for this purpose any of the materials and methods well known in the art.

A ring-shaped control electrode I2 is positioned immediately before the concave surface I, a lead I 4 sealed through the press 4 acting as a support and providing an external connection through which signal current may be. led from a blocking condenser I5 connected to an antenna It or other source.

In registry with cathode 5 and control electrode I2 is positioned a gun type anode I'I positively energized from a d.-c.' potential source I9 through a supporting lead sealed through the press 4. The gun thus formed is in axial alinement with a multiplying chamber formed by a cylindrical collecting anode supported by a lead 26 sealed through said envelope I. Concen- 25 trically within anode 25 is a cathode screen 21 formed of fine wire gauze sensitized for photoemission and to provide a high secondary emission ratio and supported by a lead 29 sealed through the envelope I. The screen is preferably formedof fine, woven silver wire, but may also be made by punching out a sheet or any other known method for producing a finely apertured structure in which the ratio of apertured area to total area is of the order of one to four.

The silver may be oxidized, or coated with caesium which in turn is oxidized, to increase the ratio of secondary emission. Any of the photoemission-aiding and emission ratio increasing means known in the art are deemed a full equivalent of this cathode structure treating method.

concentrically within cathode 27 is a hellcal accelerating anode 30 supported by a lead 3| sealed through the envelope I. Anode 30 may be formed by winding spaced turns of wire into a helix, and maintaining the separation between adjacent turns by spot welding to spacing rods 32 evenly spaced within the periphery of the helix parallel to the axis thereof.

In operation, the current to be amplified is applied to a carrier input circuit 35, to which is inductively coupled an amplifier input coil 36 tuned bya variable capacitance 31 shunted thereacross. Oneside of coil 36 is connected through lead 29 to the secondarily emissive and photosensitive cathode screen 21. The other side of coil 36 is grounded and connected through a. blocking condenser 39 to the accelerating anode so through lead 3|. To the anode 30 is also connected the positive terminal of a source 40 of steady d.-c., the negative terminal of which is grounded.

A positive potential is also applied to collect ing anode through lead 26 from a d.-c. source 4|, the negative pole of which is also grounded. Between source M and lead 26 is inserted an output coil 42 tuned by a variable capacitance l4, and having inductively coupled thereto a coil 45, from which the amplified and modulated carrier output may be taken for further use.

If, now, a carrier be applied to coil 35, an alternating potential will be set up between the accelerating anode and the cathode screen, in addition to the d.-c. potential on anode 30, reaching its full valuewhen the capacitance 31 is adjusted to make the amplifier input circuit resonate at the carrier frequency.

Free electrons in the multiplying space will be attracted by the positive potential on the anode 30, but due to the small area presented by the anode, the greater number of electrons will pass through and continue toward the screen 21, on which the greater number will strike, producing I secondaries. Some will pass through,

' however, the ratio being very nearly that of the capacitance 44.

apertured area to the total area, or one to four.

Those electrons passing through will be further accelerated by the potential on collecting anode 25, and on collection will flow of! through the output circuit including coil 42 and variable When the carrier frequency is raised above ten megacycles it is found necessary to provide a source of electrons in order that multiplication may reach satisfactory current values in the time available, and for this purpose it is possible to direct a, light upon the photosensitive cathode. The photo-emission produced thereby permits current to build up rapidly, the current being in its maximum value a linear function of the illumination intensity up to the point of space change saturation. The light source and the optical system for focusing its rays upon the cathode are not shown in the figure. however, inasmuch as I preferably utilize an electron gun as described above, since it possesses advantages in regard to modulation.

Returning now to the point where the electrons supplied by the source are accelerated by the anode 30, pass therethrough and produce secondaries by impact on. the cathode screen, it will be seen that while a carrier is applied between cathode 21 and anode 30, there will be a continuously varying potential therebetween, fluctuating in value about the d.c. potential difference due to source 40. The paths followed by the secondaries will depend upon these changing potentials. If the particular electrons are knocked out of the cathode when the anode'30 is least positive, the potential on collecting anode 25 will be controlling, and the electrons will be drawn thereto and collected. I

If the electrons commence their flight from the screen cathode when the anode 30 is most positive, some of them will be attracted back toward it, pass therethrough, and repeat the-secondary producing impact on the screen cathode. Others will pass immediately through the screen and be collected on anode'25. By proper adjustment of the potentials, repeated multiplication producing trips into and out of thespace permeable accelerating anode bounded by the anode may be secured, and as is now well known in the art, a greatly amplified output current secured. The output may be usefully applied from inductance 42 in the collecting anode circuit.

The output current is linearly proportional to the electron supply at the beginning of each cycle, as stated with reference to the photosensitive cathode as described above. and so by applying a signal current to the control electrode 12 of the electron gun, the carrier will be modulated thereby. It will thus be seen that the device herein presented affords a simple method of modulating a signal current on a radio-frequency carrier, and greatly amplifying the modulated carrier.

Thefollowing is claimed:

1. A radio-frequency tube having an evacuated envelope containing an electron gun comprising a cathode and an anode cooperating when'energized to produce an electron beam, a control electrode between said cathode and anode, means for applying a multipactor amplifier signal current to said control electrode, and a multiplying chamber in registry with said gun, including a. cylindrical collecting anode adapted to be positively energized by asteady source of d.-c., a secondarily-emissive electron-permeable cylindrical cathode held concentrically within said collecting anode, and a cylindrical electronconcentrically placed within said cylindrical cathode and adapted to be positively energized.

2. A radio-frequency multipactor amplifier tube having an evacuated envelope containing an electron gun comprising a cathode and an anode cooperating when energized to produce an electron beam, a control electrode between said cathode and anode, means for applying a signal current to said control electrode, and a multiplying chamber in registry with said gun, including a cylindrical collecting anode adapted to be positively energized by a steady source of d.-c., a photosensitive secondarily-emissive electron-permeable cylindrical cathode held concentrically within said collecting anode, and a cylindrical electron-permeable accelerating anode concentrically placed within said cylindrical cathode and adapted to be positively energized.

3. A radio-frequency multipactor amplifier tube comprising an evacuated envelope having therein a collecting anode adapted to be positively energized, an electron-permeable secondarily emissive cathode within said collecting anode, an electron-permeable accelerating anode within said cathode adapted to be positively energized, an electron gun in registry with said accelerating anode, comprising a cathode and an apertured anode arranged when energized to produce an electron beam, and a control electrode arranged to be energized by a'signal current.

4. A radio-frequency multipactor amplifier tube, comprising an evacuated envelope having therein a cylindrical collecting anode arranged to be positively energized, an electron-permeable photosensitive secondarily emissive cylindrical cathode concentrically placed within said collecting anode, a helical accelerating anode concentrically supported within said cathode and arranged to be positively energized, and an electron gun positioned to direct, when energized, a beam of electrons into said helical anode, said gun having a control electrode arranged to be energized by signal potentials;

5. A radio-frequency multipactor amplifier,

meable secondarily emissive cathode concentric" including an evacuated envelope having therein an accelerating helical anode, an electron-per-' meable secondarily emissive cathode concentric thereabout, a cylindrical collecting anode concentrically placed about said cathode, an electron beam source having a control electrode and arranged to direct electrons into said helical anode,

leads sealed through said envelope to said elec-- tron beam source and said control electrode, means connected with said leadsfor energizing said source, means for applying signal potentials to said control electrode through said lead thereto, leads sealed throng said envelope to said accelerating anode, said secondarily emissive cathode, and said collecting anode, a variable input impedance connected in series with a blocking condenser across, said cathode and said helical anode, a carrier frequency input circuit coupled to said variable input impedance, a d.-c. potential source having'its positive connected to said accelerating anode lead and its negative grounded, a variable output impedance connected to said collecting anode lead, an output work circuit coupled to said output impedance, and a positive d.-c. source, having its negative end grounded, connected through said variable out put impedance to said collecting anode.

6. A radio-frequency multipactor amplifier, including an evacuated envelope having therein an accelerating helical anode, an electron-perthereabout, a cylindrical collecting anode concentrically placed about said cathode, an electron beam sourceshaving a control electrode and arranged to direct electrons into said helical anode, leads sealed through said envelope to said electron beam source and said control electrode, means connected with said leads for energizing said source, means'for applying signal potentials to said control electrode through said lead thereto, leads sealed through said envelope to said accelerating anode, said secondarily emissive cathode and said collecting anode, a variable input impedance connected in series with a blocking condenser across said cathode and said helical anode, a carrier frequency input circuit coupled to said variable input impedance whereby said accelerating anode and said secondarily emissive cathode may be energized in opposite phase by a carrier current, a d.-c. potential source having its celerating anode lead'and its negative grounded, a variable output impedance connected to said collecting anode lead, an output work circuit coupled to said output impedance, and a positive d.-c. source, having its negative end grounded,

connected through said variable output impedance to said collecting-anode.

PHILO 'r. imainswoa'rn.

positive connected to said ac- 

